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Parasitic diseases of the biliary tract occur frequently in tropical and subtropical areas and cause high morbidity and mortality. In general, neither the clinical presentation nor the general laboratory findings are sufficiently unique to raise the possibility of a parasitic biliary infestation in the mind of the surgeon. Once considered, however, the presence of a parasitic biliary infestation is easily confirmed. Most commonly this is accomplished by the identification of the parasite in stools or duodenal contents. Ultrasonography, CT and MRI are not only important in the diagnosis of parasitic biliary diseases but also in the follow-up and surveillance. ERCP is an excellent diagnostic tool for demonstrating the presence of parasites in the biliary tree. Furthermore, ERCP is also used in the therapy of biliary parasitic infestations and carries less morbidity and mortality than the surgical approach. Surgery is only indicated in complicated cases. Mechanisms that may be effective against parasites include: antibodies; cytotoxic T cells; T-cell-induced activated macrophages; natural killer cells, and a variety of cells that mediate antibody-dependent cell-mediated cytotoxicity and modulators of the immune system such as cytokines. Future research has to focus on the importance of these mechanisms for the immune evasion by parasites.